Power plant variable geometry control

ABSTRACT

Means for controlling the variable geometry of a gas turbine engine having a mechanism for varying the power turbine stator geometry or the gas generator exhaust nozzle geometry to achieve maximum acceleration time by matching the geometry of the engine to the acceleration and droop schedules of the fuel control.

United States Patent [72] Inventors Louis A. Urban [56] References CitedGmby, Conn-i UNITED STATES PATENTS 3:? Swarm Lmgmeadw, 3,521,446 7/1970Maljanian.... 60/39.25 [21] AppL NO. 788,856 3,523,423 8/1970 Young60/239 3,529,419 9/1970 Reed 60/39.25 [22] F1led Jan. 3, 1969 2,857,73910/1958 Wright 60/238 [45] Paemed May 1971 2 912 824 11/1959 v N t 60/3925 [73] Assignee United Aircraft Corporation an es East Hart d C2,931,168 4/1960 Alexander 60/238 2,972,858 2/1961 Paulick 60/2383,091,080 5/1963 Crim 60/236 3,181,295 5/1965 Pauwels 60/3925 3,252,6865/ 1966 Chadwick... 60/39.25

3,348,560 10/1967 Steams 60/39.25 3,472,027 10/1969 Snow.; 60/236 54POWER PLANT VARIABLE GEOMETRY m Exami'l"Mark Newman CONTROLAttorney-Laurence A. Savage 10 Claims, 5 Drawing Figs. s

[5 2] US. Cl 60/239, ABSTRACT: Means for controlling the variablegeometry of a 60/39.25 gas turbine engine having a mechanism for varyingthe power [51] Int. Cl F02k l/16, turbine stator geometry or the gasgenerator exhaust nozzle F02k ll] 8 geometry to achieve maximumacceleration time by matching [50] Field of Search 60/3925, the geometryof the engine to the acceleration and droop 235, 236, 237, 238, 239schedules ofthe fuel control.

1 j/ FROM HIGH PRESSURE SOURCE OPEN llll/I/I/Iflll/I/I/II/l/I/l/ll/I/I/I/l/WWII/[ l f l FU EL C ON TROL l l V W .1AFEEDBACK VALVE l I l I V f I 1 7 7 l/l/l/d'l W4 M w Z/ &2 P SS rFwfignoi op FROM HIGH T I.T.OR PRESSURE v, o THE ACCEL SOURCE W5 82SCHEDULE 4.

\ PROPORTIONAL TO g:- vgy m/lg AcTuAL-Aytg DESIRED POWER PLANT VARIABLEGEOMETRY CONTROL BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to a means for controlling the variable geometrydownstream of the hot gas generator section of a gas turbine engine andparticularly to a means for controlling the variable area geometry ofthe power turbine stator or the gas generator exhaust nozzle.

2. Description of the Prior Art The usual method of controlling thevariable area geometry of the power turbine is open loop scheduling ofthe variable area from power lever. This method has disadvantages inthat it does not recognize engine deterioration effects or engine toengine variability, which can cause the steady-state operating line tovary widely with respect to the acceleration line; it does not permitrapid acceleration or deceleration; and the inaccuracies of open loopscheduling prevent moving the steadystate operating line as close to theacceleration line as desired for most efficient engine operation.

SUMMARY OF THE INVENTION For efficient gas turbine engine operation itis desirable to maximize the engine thrust or power output and minimizethe fuel consumption. It is inherent in the gas turbine cycle that thehigher the turbine inlet temperature, the higher the thrust orhorsepower output per pound of engine air flow. Also, the higher thecycle pressure ratio, the lower the specific fuel consumption. Since atany given rotational speed a gas turbine is essentially a fixed air flowmachine, it is obvious that for optimum operation it should be made tooperate at the highest practical turbine inlet temperature and pressureratio at any particular speed. This may be accomplished by controllingthe variable area geometry downstream of the hot gas generator sectionof the engine. The hot gas generator may be any of the well known typesof gas turbine engines such as an axial or centrifugal, single or splitspool compressor; a heat source including a fuel burner, with or withouta regenerator; and a turbine or turbines to drive the compressor. Thehot gas output may go into either a free turbine with variable areanozzles to produce horsepower, or by acceleration through a variablearea exhaust nozzle'to produce thrust.

It is, therefore, an object of this invention to provide an improvedmeans for controlling the variable geometry of a gas turbine enginepower turbine which will allow the engine to operate in steady-state asclose as is prudently possible to the acceleration schedule.

Since the engine acceleration schedules are generally chosen to limiteither turbine inlet temperature (to avoid structural damage) or tolimit compressor pressure ratio (to avoid surge of the compressor), itis a further object of this invention to allow the engine to operate insteady-state at the highest practical turbine inlet temperature andcompressor pressure ratio at any particular turbine rotational speed bycontrolling the area of the turbine variable geometry.

Another object of the present invention is to provide a control for thevariable area geometry of a turbine which utilizes a schedule which isreadily available within the fuel control so that the requirement ofgenerating a schedule especially for the variable area geometry controlis obviated.

Another object of this invention is to base the signal which is utilizedfor control of the variable area geometry on any one of the well-knownparameters which may be utilized to schedule acceleration fuel flow tothe engine, such as W,/P W,/8,,, or direct sensed turbine inlettemperature, for example.

Another object of the present invention is to apply droop control to thepower turbine stator variable area or to the gas generator exhaustnozzle variable area because, as will be understood by one skilled inthe an, the acceleration capabilities of the engine will be increasedthereby.

In accordance with the present invention, an improved closed loopturbine-type of power plant variable area geometry control is providedby control means responsive to a function of the acceleration and dropschedule provided by the fuel control which senses engine operatingparameters such as turbine inlet temperature, the speed of the engine,the engine inlet temperature and the condition of the engine (i.e.,whether operating in the acceleration, steady-state or decelerationmode).

In further accord with the present invention, the function of thedesired turbine inlet temperature to which the control means isresponsive may be based on any of the parameters commonly used foracceleration scheduling of fuel; e.g., w lP W,/8 or direct sensedturbine inlet temperature. The desired turbine inlet temperature istaken as a signal from the main fuel metering control as a percentageof, or difference from, the acceleration scheduled value.

In still further accord with the present invention, droop control on thearea of the power turbine variable geometry is provided by droop controlmeans in combination with the abovementioned control means.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of a preferred embodiment thereof, as illustrated in theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a graphical illustration showingthe operating map of a gas turbine engine'with variable geometry controlover the speed range of the engine as a function of turbine inlettemperature. Point 1 represents engine idle, point 4 represents maximumengine speed, and points 2 and 3 are intermediate therebetween. All fourpoints may be positions of the power lever.

FIG. 2 is a graphical illustration showing the operating map of a gasturbine engine with variable geometry control over the speed range ofthe engine as a function of fuel flow.

FIG. 3 is a graphical illustration of the variation of the power turbinevariable geometry area over the speed range of the engine.

FIG. 4 is a schematic drawing of an exemplary embodiment of an improvedpower turbine variable geometry control in accordance with the presentinvention.

FIG. 5 is a schematic drawing of a gas turbine engine showing thelocation of the actuating means for positioning the variable powerturbine stator geometry mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 4, there isshown a control valve designated generally by numeral 2, which may beany of the types of control valves well known in the fuel control art.Translatable within a housing 4 is a spool 6 having lands 8, 10, I2 and14 thereon. A port 16 is connected to a source of fluid under highpressure, via line 18. Ports 20 and 22 are connected to drain (a lowpressure source) by lines 24 and 26 respectively. Port 28 is connected,via line 30, to variable geometry actuating means 31 which may take theform of a piston 32 which is translatable within housing 34. The piston32 is connected to a mechanism 3 (shown in FIG. 5) of any type wellknown in the art which varies the area of the power turbine variablegeometry (shown in FIG. 5) and actuates the motion thereof. Port 36 isconnected to the other side of the piston 32 by line 38. v

Also disposed on the spool is an annular groove 40; highpressure fluidflows through a fixed restriction 42, a line 44 and then into a port 46.From the port 46 the fluid flows into the groove 40, through meteringwindow 48 and into line 50 from whence it flows to a drain line 52 afterfirst flowing through a groove 54 and a metering window 56 in the valve58. The valve 58 is a droop valve of the type well known in the fuelcontrol art; the groove 54 on the spool 55 is positioned by comparingactual corrected engine speed with desired corrected engine speed. Thedescription of the droop valve is omitted herefrom for the sake ofconvenience and simplicity, but a typical type of droop valve is shownin US. Pat. No.

3,492,814 and reference is made thereto. As will be obvious to oneskilled in the art, it would only be necessary to modify droop valve 76(shown in U.S. Pat. No. 3,492,814) by adding metering window 56 andgroove 54 thereto, to obtain the droop function.

High-pressure fluid is also metered through a fixed restriction 60, aline 62, a line 64 and into a metering port '66 of turbine variablegeometry feedback valve 68. The valve 68 is positioned in response tothe position of the variable geometry control actuator piston 32.Pressure in line 84 is ported by a metering port 74 in the valve 68 toline 76. The pressure in the line 84 will be intennediate the pressuresmetered by the ports 66 and 74, and it is connected to a chamber 80 of aleast pressure selector 82 via line 84. The least pressure selector 82compares the pressure signal fed by line 84 with the pressure in line 50intermediate metering window 48 and metering window 56 which is fed to achamber 86 of the least pressure selector 82 via line 87. The leastpressure selector 82 selects the lower of these two pressure signals andfeeds it, via line 88, to a chamber 90 of a most pressure selector 92.Obviously, from an inspection of FIG. 3 is will be appreciated that theleast pressure selector 82 serves to set the limits so that during anacceleration and deceleration condition the nozzles will not go aboveand below a predetermined value.

High-pressure fluid flowing through the fixed restriction 60 and line 62also flows through a line 94, a fixed restriction 96 and into a line 98;from the line 98 the fluid normally flows through a retard solenoidvalve 100, via a line 102, from which it flows to drain via line 78; thepressure in line 98 is fed to the chamber 90 of the most pressureselector 92 where its pressure is compared with the pressure is comparedwith the pressure in line 88. The most pressure selector 98 selects thehigher of these two pressures and transmits a signal indicative of thispressure to end 104 of the spool 6 via line 106. A pressure signal fromthe acceleration schedule of the fuel control 5 is fed to the end 108 ofthe spool 6. An example of a pressure signal from the accelerationschedule of a fuel control that can be utilized with the presentinvention is shown in US. Pat. No. 3,348,560 which is hereinincorporated by reference. Specifically, the pressure in line 266 of the3,348,560 patent, supra, can be utilized for this purpose.

The system operates to reset the piston 32 until the pressures on ends104 and 108 of the spool 6 are equal and the spool 6 is in balance.

The operation of a gas turbine engine incorporating the control forvarying the area of the power turbine variable geometry according to thepresent invention will be explained with reference to the FIGS. Since aturboshaft engine is shown for the purpose of describing a preferredembodiment, the geometry which is varied to attain the objects of thisinvention is that of the power turbine stator. However, it will readilybe understood by those skilled in the art that if the engine is astraight jet, the gas generator exhaust nonle geometry will be varied toprovide optimum engine performance.

To more fully understand the following description of the operation of agas turbine engine incorporating our novel control (which descriptionrefers to various FIGS.) the following symbols are defined:

Symbol Definition Assume as a starting point that the engine is idling(points 1 on FIG. 1 through FIG. 3). If the power lever is suddenlyshifted to a position represented by points 2, the valve means 2 willreceive a change in pressure signal from the droop valve 58 on the end104 of the spool 6 through selectors 82 and 90. The signal received willshift the spool towards the right, thereby uncovering land 36 on thehigh-pressure fluid port 16. Fluid flows into the line 38 via port 36and into the chamber 33 in the cylinder 34. Fluid in the chamber 35flows out through the line 30, through the port 28 and into the port 20from which it flows to the drain line 52 via line 24. The piston 32 willthus move to the right, opening the area of the power turbine variablegeometry (shown best in FIG. 5). As shown in FIG. 2, the fuel flow willincrease to point 5 and will follow the acceleration schedule to point6, from where it will follow the droop line a down to point 2. Likewisein FIG. 3, the variable geometry area will open to the stop line atpoint 5, follow the stop line to point 6 where it intersects droop lineor and then close to point 2 by following the droop line a from point 6to point 2. As will be understood by those skilled in the art, theengine accelerates faster because of the droop on the variable area. Ifdroop were not provided and the area simply scheduled by the powerlever, the area would close to point 2 immediately upon the power leverbeing moved and the engine acceleration time would be longer. As thepiston 32 moves open and then towards closed as shown in FIG 3, thefeedback valve 68 moves in relationship thereto. High-pressure fluid inthe line 64 is metered by the port 66 of the valve 68 into the chamberof the least pressure selector via the line 84. During acceleration thepressure in the chamber 86 will be greater than the pressure in thechamber 80, and, therefore, the least pressure selector will select thepressure in the chamber 80 and transmit it, via the line 88, to thechamber of the most pressure selector 92. Since the solenoid valve isopen at all times except for deceleration, the pressure in the line 88is greater than the pressure in the line 98. Therefore, the pressurefrom the line 88 will be transmitted, via the line 106, to the end 104of the spool 6. The piston 32 will move until the pressure on the end104 equals the pressure on the end 108 of the spool 6. The spool willthen move to the null position, thus closing the ports 28, 36 and 46 andstopping movement of the piston 32.

During steady-state operation of the gas turbine engine the droop valve58 controls the position of the piston 32. The position of the groove 54within the window 56 is determined by pressure signals in the maincontrol being fed to the ends of the spool 55. The signal fed to one endof the spool 55 is a function of the actual corrected speed, while thesignal fed to the other end of the spool is a function of the desiredcorrected speed. Fluid from the high-pressure source flows to the drainline 52 via restriction 42, line 44, groove 40 in the window 48, line 50and the droop valve 58. The pressure intermediate the two variableorifices is fed, via the line 87 to the chamber 86. Since the pressurein the chamber 86 is less than the pressure in the chamber 80 duringsteady-state operation, the least pressure selector 82 will transmit thepressure in the chamber 86 to the chamber 90 of the most pressureselector 92 via the line 88. From chamber 90 that pressure is fed to theend 104 of the spool 6 via the line 106. A pressure signal indicative ofthe acceleration schedule is also fed to the end 108 of the spool 6 bythe fuel control. As described above, the spool 6 will move ofi the nullposition and the piston 32 will thereby be moved until the pressuresignals on ends 104 and 108 of the spool 6 are equal at which time thespool 6 will move back to the null position and halt movement of thepiston 32. That condition will occur when the actual corrected speed isequal to the desired corrected speed.

During deceleration, the solenoid vale 100 is closed. When the solenoidvalve 100 closes, the pressure in the line 98 will be the highestpressure being fed to the chamber 90 of the most pressure selector 98and will, therefore, be transmitted to the end 104 of the spool 6 viathe line 106. This pressure will force the spool 6 to the left, therebydirecting high-pressure fluid into the chamber 35 of the actuating means31 and connecting the chamber 33 to drain. The piston 32 will then movetowards the left which closes the power turbine variable area in orderto rapidly decelerate the engine. When the pressures on the ends 104 and108 are equal, the spool 6 will again return to the null position, thusstopping motion of the piston 32.

There has thus been described a preferred embodiment of a fuel controlin accordance with the present invention. It should be understood bythose skilled in the art that various changes and omissions in the formand detail thereof may be made therein without departing from the spiritand scope of the invention, which is to be limited only as set forth inthe following claims:

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. Means for controlling the variable geometry of gas turbine enginehaving a mechanism for varying the power turbine stator geometry or thegas generator exhaust nozzle geometry and having a fuel control forregulating the flow of fuel thereto, comprising:

actuating means connected to said mechanism for changing the variablegeometry;

first computing means for selecting the higher of two pressure signalsfed thereto;

second computing means for selecting the lower of two pressure signalsfed thereto, the output of said second computing means being fed to saidfirst computing means as one of said two pressure signals;

feedback valve means responsive to the position of said actuating meansfor metering hydraulic fluid pressure to said second computing means asone of said two pressure signals;

a first control valve responsive to the position of a servovalve formetering hydraulic fluid;

a second control valve responsive to the speed error between the actualcorrected speed and the desired corrected speed of the gas turbineengine for metering hydraulic fluid, said second control valve disposedin series with said first control valve, the fluid pressure between saidcontrol valves being fed to said second computing means as the other ofsaid two pressure signals;

normally open solenoid valve means for metering hydraulic fluid pressureto said first computing means as the other of said two pressure signals,said solenoid valve closing in response to deceleration of the gasturbine engine; and

servovalve means responsive to a function of the acceleration fuel flowto the gas turbine engine and to a signal, which is the higher of thetwo pressure signals, from said first computing means for controllingthe position of said actuating means.

2. For a gas turbine type of power plant having variable area geometryand having a fuel control that includes means responsive to power plantoperating conditions including a power lever, said fuel control having aspeed droop on area control responsive to said power lever forscheduling the steady state and acceleration operation thereof, incombination with:

closed loop control means including means responsive to saidacceleration schedule and said speed droop on area control for producinga first control signal for controlling the area of said variablegeometry of the power plant; and feedback means responsive to thegeometry change of said power plant for producing a second signal, saidsecond signal modifying said first signal to limit nozzle area so as tomaintain the operating conditions of the power plant at a predeterminedvalue relative to said acceleration schedule. 3. For a gas turbine typeof power plant as claimed in claim 2 in which the steady state operationis obtained by a speed droop on fuel flow control and said closed loopcontrol means responds to said area droop control, said area droopcontrol being matched to said droop schedule of said fuel control.

4. or a gas turbine type of power plant as clalmed 1n clatm 2 whereinsaid power plant operating conditions includes a function of turbineinlet temperature.

5. For a gas turbine type of power plant as claimed in claim 4 whereinsaid power plant operating conditions includes the power plant inlettemperature, the speed in revolutions per minute of the power plant andanother condition of said power plant.

6. For a gas turbine type of power plant as claimed in claim 3 whereinsaid speed droop control includes means responsive to the differencebetween the actual speed in revolutions per minute of said power plantand the desired speed in revolutions per minute of said power plant.

7. For a gas turbine type of power plant as claimed in claim 3 whereinthe variable geometry is the turbine stator.

8. For a gas turbine type of power plant as claimed in claim 3 whereinthe variable geometry is the power plant exhaust nozzle.

9. For a gas turbine type of power plant as claimed in claim 3 includinga hydraulic circuit, a source of high pressure and a drain, an actuatorconnected to the variable area geometry, valve means being positioned bya pressure signal indicative of said acceleration schedule and anopposing pressure signal indicative of the area of said variable areageometry for regulating the egress and ingress of flow from said sourceto drain to and from said actuator for controlling the position thereof.

10. For a gas turbine type of power plant as claimed in claim 9including a droop valve connected to said valve means for furtheradjusting said opposing pressure signal to further control said valvemeans so as to effectuate changes of the position of said actuator.

1. Means for controlling the variable geometry of gas turbine enginehaving a mechanism for varying the power turbine stator geometry or thegas generator exhaust nozzle geometry and having a fuel control forregulating the flow of fuel thereto, comprising: actuating meansconnected to said mechanism for changing the variable geometry; firstcomputing means for selecting the higher of two pressure signals fedthereto; second computing means for selecting the lower of two pressuresignals fed thereto, the output of said second computing means being fedto said first computing means as one of said two pressure signals;feedback valve means responsive to the position of said actuating meansfor metering hydraulic fluid pressure to said second computing means asone of said two pressure signals; a first control valve responsive tothe position of a servovalve for metering hydraulic fluid; a secondcontrol valve responsive to the speed error between the actual correctedspeed and the desired corrected speed of the gas turbine engine formetering hydraulic fluid, said second control valve disposed in serieswith said first control valve, the fluid pressure between said controlvalves being fed to said second computing means as the other of said twopressure signals; normally open solenoid valve means for meteringhydraulic fluid pressure to said first computing means as the other ofsaid two pressure signals, said solenoid valve closing in response todeceleration of the gas turbine engine; and servovalve means responsiveto a function of the acceleration fuel flow to the gas turbine engineand to a signal, which is the higher of the two pressure signals, fromsaid first computing means for controlling the position of saidactuating means.
 2. For a gas turbine type of power plant havingvariable area geometry and having a fuel cOntrol that includes meansresponsive to power plant operating conditions including a power lever,said fuel control having a speed droop on area control responsive tosaid power lever for scheduling the steady state and accelerationoperation thereof, in combination with: closed loop control meansincluding means responsive to said acceleration schedule and said speeddroop on area control for producing a first control signal forcontrolling the area of said variable geometry of the power plant; andfeedback means responsive to the geometry change of said power plant forproducing a second signal, said second signal modifying said firstsignal to limit nozzle area so as to maintain the operating conditionsof the power plant at a predetermined value relative to saidacceleration schedule.
 3. For a gas turbine type of power plant asclaimed in claim 2 in which the steady state operation is obtained by aspeed droop on fuel flow control and said closed loop control meansresponds to said area droop control, said area droop control beingmatched to said droop schedule of said fuel control.
 4. For a gasturbine type of power plant as claimed in claim 2 wherein said powerplant operating conditions includes a function of turbine inlettemperature.
 5. For a gas turbine type of power plant as claimed inclaim 4 wherein said power plant operating conditions includes the powerplant inlet temperature, the speed in revolutions per minute of thepower plant and another condition of said power plant.
 6. For a gasturbine type of power plant as claimed in claim 3 wherein said speeddroop control includes means responsive to the difference between theactual speed in revolutions per minute of said power plant and thedesired speed in revolutions per minute of said power plant.
 7. For agas turbine type of power plant as claimed in claim 3 wherein thevariable geometry is the turbine stator.
 8. For a gas turbine type ofpower plant as claimed in claim 3 wherein the variable geometry is thepower plant exhaust nozzle.
 9. For a gas turbine type of power plant asclaimed in claim 3 including a hydraulic circuit, a source of highpressure and a drain, an actuator connected to the variable areageometry, valve means being positioned by a pressure signal indicativeof said acceleration schedule and an opposing pressure signal indicativeof the area of said variable area geometry for regulating the egress andingress of flow from said source to drain to and from said actuator forcontrolling the position thereof.
 10. For a gas turbine type of powerplant as claimed in claim 9 including a droop valve connected to saidvalve means for further adjusting said opposing pressure signal tofurther control said valve means so as to effectuate changes of theposition of said actuator.